In general, the real state of chemotherapy of cancer is such that it is difficult to obtain sufficient therapautic effect because of toxicity and side effects of medicines. Particularly, there are few medicines which are effective against solid cancer and, therefore, development of a medicine which is effective against solid cancer but has high safety is an urgent technical subject in this art.
In this respect, a flavone acetic acid of the formula II: ##STR2## is noted as a compound effective against solid cancer such as colon 38 and the like in an animal test [Daniel S. Zaharka et al., Cancer Treatment Reports, 70, 1415 (1986); Japanese Patent Laid Open Publication No. 58-96082 (corresponding to AU-8290-728); Eur. J. Med. Chem. Chim. Ther., 1985-20, No. 5, pp393-402]. However, in order to use this compound as a medicine practically, it seems that it is necessary to further improve usefulness thereof, for example, by further enhancing its antitumor activity and making its side effect weaker.